# Polyurethane Foaming Technology Polyurethane (PU) is a versatile material with excellent properties, widely used in various industries such as automotive, household appliances, construction, electronics, footwear, packaging, helmets, sports equipment, and more. Polyurethane foaming agent is the most important additive in PU foam plastics, which directly affects the physical and mechanical properties, foam density, temperature resistance, and other aspects of PU foam. The foaming agents used to produce PU foam are usually divided into two types: chemical foaming agents and physical foaming agents. ## Chemical foaming agents Chemical foaming agents are gases produced by chemical reactions (water and isocyanate react to release CO₂) that make polyurethane foam. Examples are water, formic acid, higher organic acids (carboxylic acids), etc. ## Physical foaming agents Physical foaming agents are vaporized by the heat generated by the polyurethane polymerization reaction, making polyurethane foam. ## The evolution of foaming agents The first generation of foaming agents: low-boiling hydrocarbon compounds, mainly CFC-11, CFC-12, etc. In recent years, it has been found that these compounds are the culprit of destroying the earth’s ozone layer. After the fluorochlorocarbons enter the stratosphere, they are exposed to intense ultraviolet rays and release chlorine atoms, which cause the ozone layer to break and form ozone holes, endangering the survival of humans and other organisms. They were completely banned in 2010. The second generation of foaming agents: HCFCs (HCFC-141b difluorodichloroethane), with ideal thermal conductivity values, do not require major changes in production processes, and are widely used. However, they have high prices, and to achieve the same insulation effect as CFC-11, the foam density needs to be increased by about 10%; HCFCs have ODP values (ozone depletion potential), which still cause damage to the ozone layer. They are only a transitional foaming agent and will be gradually restricted to banned. The third generation of foaming agents: They are green foaming agents with performance close to CFC-11 and ODP (ozone depletion potential) of zero, such as HFCs, liquid CO₂, pentane series, etc. The pentane series includes cyclopentane, isopentane, and n-pentane (C5H12), which have an ODP (ozone depletion potential) value of zero, a low GWP (global warming potential) value, low toxicity, and little impact on the environment. At present, developed countries have fully applied the third-generation foaming agents. The domestic polyurethane industry started late, and small and medium-sized manufacturers of PU polyurethane composite panels are still using the second generation. Baoye Group’s Italian fully automatic composite panel production line in the Economic Development Zone of Deyang City, Sichuan Province uses the third-generation n-pentane series from Junyuan Petroleum Group, which is green and environmentally friendly, and contributes more to the realization of the country’s “carbon peak and carbon neutrality” dual carbon goals. ## N-pentane polyurethane foaming technology ### The characteristics of n-pentane Appearance and properties: colorless transparent liquid, with a faint aromatic odor. Melting point (℃): -129.8 Relative density (water=1): 0.63 Boiling point (℃): 36.1 Relative vapor density (air=1): 2.48 Critical temperature (℃): 196.4 Critical pressure (MPa): 3.37 Flash point (℃): -40 Explosion upper limit (%): 7.8 Ignition temperature (℃): 260 Explosion lower limit (%): 1.5 It is mainly used in the continuous production line of polyurethane panels, as polystyrene foaming and polyurethane foaming. ### The requirements of n-pentane for equipment 1. Because n-pentane is flammable, explosive, and volatile, it has special requirements for pumps and pipelines. For users with large production volume, it is recommended to use underground storage tanks. 2. During the production process, to prevent n-pentane leakage, ventilation should be paid attention to at all times, and n-pentane leakage sensors should be installed in the main positions. 3. The metering device should be installed in a separate ventilated room and equipped with a n-pentane leakage sensor. The pre-pressure and high-pressure of the pump should be equipped with detection devices. 4. The equipment should meet the requirements of producing high flame retardant (PIR) double-track of more than 30 meters. ### The advantages of n-pentane foaming technology 1. Compared with cyclopentane, n-pentane has better foam size stability. After the panel is formed, the shrinkage of the panel in the thickness and width directions is smaller than that of cyclopentane foam. 2. N-pentane foaming products have higher compressive strength in the thickness direction than cyclopentane and HCFC-141b foaming products. The compressive strength of PIRI can reach 182kPa. 3. Under almost the same foam core density, the feed density of the n-pentane foaming formula is lower. This means that the feed amount is reduced, the foam cost has a downward trend, and the compressive strength of the foam can reach the same or higher level. 4. Because HCFC-141b is highly polar and hydrophilic, n-pentane is weakly polar and oleophilic, and isocyanate is also oleophilic, n-pentane has better solubility with isocyanate, and the emulsification effect is better during high-pressure mixing in production. Therefore, the hard foam after n-pentane foaming has uniform and finer pores. 5. After a certain formula adjustment, the flame retardant performance of the n-pentane foaming product can reach or exceed the HCFC-141b foaming product. 6. The thermal insulation performance of the polyurethane rigid foam made by using n-pentane as a foaming agent can meet the thermal insulation performance requirements of cold storage panels. Foaming agents are related to the molding and insulation of polyurethane foam, which affects the product quality; they are also related to human protection of the atmosphere and the impact on climate change.
